Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$186.83	12.665%	$210.492	$210.49	$210.50	$210.50
Purchase #2	$22.54	13.305%	$25.5389	$25.54	$25.55	$25.50
Purchase #3	$175.64	10.752%	$194.5248	$194.52	$194.50	$194.50
Purchase #4	$50.90	12.298%	$57.1597	$57.16	$57.15	$57.20
Purchase #5	$111.64	13.215%	$126.3932	$126.39	$126.40	$126.40
Purchase #6	$54.44	9.436%	$59.577	$59.58	$59.60	$59.60
Purchase #7	$99.99	4.822%	$104.8115	$104.81	$104.80	$104.80
7 purchase totals =	$701.98		$778.4971	$778.49	$778.50	$778.50